The subject matter herein relates generally to radio-frequency (RF) power generators and, more particularly, to mechanisms and methods for reducing electromagnetic radiation leakage.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that accelerates a beam of charged particles (e.g., H− ions) and directs the beam into a target material to generate the isotopes. The cyclotron includes a particle source that provides the particles to a central region of an acceleration chamber. The cyclotron uses electrical and magnetic fields to accelerate and guide the particles along a predetermined orbit within the acceleration chamber. The magnetic fields are provided by electromagnets and a magnet yoke that surrounds the acceleration chamber. The electrical fields are generated by a pair of radio frequency (RF) electrodes (or dees) that are located within the acceleration chamber. The RF electrodes are electrically coupled to an RF power generator that may include, for example, oscillators, amplifiers, control circuitry, and power supplies. The RF power generator energizes the RF electrodes to provide the electrical field. The electrical and magnetic fields within the acceleration chamber cause the particles to take a spiral-like orbit that has an increasing radius. When the particles reach an outer portion of the orbit, the particles are directed toward the target material for radioisotope production. In addition to controlling the orbit of the particles, the RF electrodes may be used to pull the particles from a particle source in the acceleration chamber.
To operate the RF electrodes within the acceleration chamber, a considerable amount of electric power (e.g., 5 kilowatts to 2 megawatts) is generated by the RF power generator. The RF power generator includes, among other things, an enclosure having a RF amplification system that includes a power electron vacuum tube. The power electron vacuum tube may be, for example, a triode, tetrode, or pentode. The RF amplification system may include a pair of resonators that each have an inner conductor and an outer conductor.
The various electrical devices and sub-systems of the RF power generator produce electromagnetic radiation (or emissions). The resonators, in particular, may generate a significant amount of radiation. Regulations and/or customer demands exist that may require the RF power generator to be electromagnetically compatible such that the RF power generator is able to reliably operate in its intended environment without leaking unwanted electromagnetic radiation that can be harmful to other electrical components. It can be challenging, however, to design RF power generators that are able to reduce the amount of electromagnetic radiation to an acceptable level. For example, RF power generators typically have a number of openings, such as passages or feedthroughs (e.g., for receiving electrical cables or water hoses), vents (e.g., for air intake or exhaust), or holes for receiving hardware (e.g., screws). These openings may allow unwanted electromagnetic radiation to leak into the exterior or into compartments where other electrical components are operating.
RF power generators often include a directional coupler that measures forward and reflected power along the coaxial line. The forward and reflected power may be monitored to control performance of the RF power generator. The directional couplers are typically positioned outside of an enclosure of the RF power generator that surrounds the resonators. The directional couplers may also produce unwanted electromagnetic radiation. In one known system, the directional coupler is positioned within the enclosure. Although the directional coupler is effective in monitoring the forward and reflected power along the coaxial line, the directional coupler is a complex assembly having several, large interconnected parts, elongated seams, and screws. Such assemblies may permit the electromagnetic radiation to leak into the exterior.